This invention relates to organometalloid compounds and metal complexes thereof, which are of use for chemical vapor deposition processes and in other chemical processes.
As the microelectronics industry moves into ultralarge scale integration (ULSI), enhancement in performance speeds of integrated circuits will be achieved by reducing the device feature size and thereby the overall die size. As a result, density constraints will require multilevel structures with vertical interconnects. It is expected that the use of metals with lower resistivity, such as gold, silver and especially copper, will be necessary because of the submicron geometries.
Fabrication of interconnect structures includes one or more metallization steps. Metallization is commonly accomplished by physical vapor deposition (PVD) processes, including evaporating and sputtering. Chemical vapor deposition (CVD) processes have an advantage over these so-called xe2x80x9cline of sightxe2x80x9d processes in the fabrication of submicron vertical interconnects because conformal layers of metals are more easily produced.
In CVD, a volatile precursor, usually a complex of a metal with an organic ligand, serves as a source of the metal. The precursor is delivered to the substrate in the vapor phase and decomposed on the surface to release the metal. The precursor must exhibit sufficient thermal stability to prevent premature degradation or contamination of the substrate and at the same time facilitate easy handling. Vapor pressure, the adsorption/desorption behaviour, the chemical reaction pathways, and the decomposition temperature can directly affect the purity of the deposited metal film and the rate of thin-film formation.
CVD precursors very frequently are based on complexes of metals with xcex2-diketonates such as 2,2,6,6-tetramethyl-3,5-heptanedione (thd) and acetylacetonate (acac) and fluorinated b-diketonates, such as 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (hfa or hfac) and 2,2-diethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedione (fod). Volatility of the non-fluorinated precursors is insufficient for many applications. The fluorinated analogs possess greater volatility, but also have a tendency to fragment, a consequence of fluorine migration/carbon-fluorine bond cleavage at elevated temperatures, leading to contamination of the substrate. Consequently, a need exists for precursors which retain volatility yet release the metal without degradation of the ligand and for ligands which are not labile or disposed toward fragmentation.
It is therefore an object of this invention to develop metal complexes for CVD precursors that are highly volatile and yet stable at the sublimation point and also retain desirable processing features. It is a further object to develop ligands for use in CVD precursors which can induce high volatility in a metal and can release the metal without degradation of the ligand. It is a further object to provide new synthetic routes for the synthesis of these ligands from commercially available starting materials in good yields.
It has been surprisingly discovered that certain organic compounds containing silicon, germanium, tin or lead, when complexed with a metal, can induce high volatility in the metal complex. The resulting complexes are stable at the sublimation point and retain desirable processing features. The compounds have the structure of formula I: 
wherein
R1 is C2 or higher alkyl, substituted alkyl, haloalkyl, cycloalkyl, C7 or higher aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, acyl, alkyl carboxylate, aryl carboxylate, alkenyl, alkynyl, or E2(R6)(R7)(R8);
R2 is H, halogen, nitro, or haloalkyl;
E1 and E2 are independently Si, Ge, Sn, or Pb;
R3, R4, R5, R6, R7, and R8 are independently chosen from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, arylalkyl, alkoxy, alkenyl, alkynyl or R4 and R5, or R7 and R8 taken together form a divalent alkyl radical;
Y and Z are independently O, S or NR9; and
R9 is alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, alkenyl, or alkynyl.
The present invention also relates to metal-ligand complexes that are highly volatile and yet stable at the sublimation point. The complexes also retain desirable processing features. The metal complexes of the present invention have the structure of formula II:
MLnxc2x7pDxe2x80x83xe2x80x83(II)
wherein
M is a metal chosen from the group consisting of: Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Y, La, Ce, Ti, Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, Mo, W, Mn, Re, Sm, Fe, Ru, Eu, Os, Co, Rh, Ir, Gd, Ni, Pd, Pt, Tb, Cu, Ag, Au, Dy, Ho, Al, Ga, In, Tl, Er, Ge, Sn, Pb, Tm, Sb, Bi, Yb, Lu, Th, and U;
D is a neutral coordinating ligand;
n is equal to the valence of M;
p is zero or an integer from 1 to 6; and
L is a compound of formula III: 
wherein
R1 is alkyl, substituted alkyl, haloalkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, acyl, alkyl carboxylate, aryl carboxylate, alkenyl, alkynyl, or E2(R6)(R7)(R8);
R2 is H, halogen, nitro, or haloalkyl;
E1 and E2 are independently Si, Ge, Sn, or Pb;
R3, R4, R5, R6, R7, and R8 are independently chosen from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, arylalkyl, alkoxy, alkenyl, alkynyl or R4 and R5, or R7 and R8 taken together form a divalent alkyl radical;
Y and Z are independently O, S or NR9; and
R9 is alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, alkenyl, or alkynyl.
In another aspect, the present invention relates to a method of depositing a metal-containing layer on a substrate comprising vaporizing a metal-ligand complex of formula II and decomposing the metal-ligand complex in the presence of the substrate.
In yet another aspect, the present invention relates to ligands having haloalkyl-substituted metalloid substituents, particularly fluoroalkyl-substituted. In this case, R3, R4, R5, R6, R7, and R8 are independently alkyl or haloalkyl, and at least one of R3, R4, R5, R6, R7, and R8 is haloalkyl.
New synthetic routes for the synthesis of the ligands of formula I from commercially available starting materials in good yields have been discovered. In yet another aspect, the present invention relates to processes for preparing the ligands of formula I and metal complexes of formula II.
The present invention relates to organometalloid compounds that confer volatility on a metal when complexed therewith. Metalloids are defined herein as the elements silicon, germanium, tin and lead. Organometalloids are defined as compounds containing one or more metalloid atoms bonded to a carbon atom. The organometalloid compounds of the present invention have the structure of formula I: 
wherein
R1 is C2 or higher alkyl, substituted alkyl, haloalkyl, haloalkyl, cycloalkyl, C7 or higher aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, acyl, alkyl carboxylate, aryl carboxylate, alkenyl, alkynyl, or E2(R6)(R7)(R8);
R2 is H, halogen, nitro, or haloalkyl;
E1 and E2 are independently Si, Ge, Sn, or Pb;
R3, R4, R5, R6, R7, and R8 are independently chosen from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, arylalkyl, alkoxy, alkenyl, alkynyl or R4 and R5, or R7 and R8 taken together form a divalent alkyl radical;
Y and Z are independently O, S or NR9; and
R9 is alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, alkenyl, or alkynyl.
In a preferred embodiment, I is a silyl xcex2-diketonate or a silyl xcex2-thioketonate and R1 is C2 or higher alkyl, C7 or higher aryl, or haloalkyl; R2 is H; R3, R4, and R5 are methyl; E1 is Si; and Y and Z are independently O or S.
In a more preferred embodiment, R1 is ethyl, isopropyl, n-propyl, isobutyl, n-butyl, t-butyl, trifluoromethyl, heptafluoropropyl, 2-propenyl or phenyl; E1 is Si; and Y and Z are O or Y is S and Z is O.
In an even more preferred embodiment the compound is one of those appearing in Table 1:
In another embodiment, R1 is methyl, ethyl, isopropyl, n-propyl, isobutyl, s-butyl, n-butyl, CF3, C2F5, i-C3F7, n-C3F7, or xe2x80x94C(CH3)(CF3)2; R2 is H; E1 is Si or Ge; R3, R4, and R5 are independently C6 or lower alkyl; and Y and Z are O. xcex1-Germa-xcex2-diketones (formula I, where E1 is Ge) are of particular interest.
In yet another embodiment, R3, R4, and R5 are independently haloalkyl or alkyl. In this embodiment, R3, R4, R5, R8, R7, and R8 are independently alkyl or haloalkyl, and at least one of R3, R4, R5, R6, R7, and R8 is haloalkyl. In particular, E1 is Si, or at least one of R3, R4, R5, R6, R7, and R8 are independently fluoroalkyl, specifically C3 or higher fluoroalkyl. The organometalloid compound may be an xcex1-sila, xcex2-diketonate wherein R1 is alkyl, or haloalkyl; R2 is H; E1 is Si; X and Y are O; and R3, R4, and R5 are independently alkyl or haloalkyl, and at least one of R3, R4, R5, R6, R7, and R8 is haloalkyl. In particular, R1 may be alkyl or haloalkyl, R3 and R4 methyl, and R5 is (CH2)2(CF2)5CF3 or (CH2)2(CF2)7CF3; in specific embodiments, R1 is methyl, n-propyl, t-butyl, CF3,C2F5, or n-C3F7.
The volatile metal complexes of the present invention are useful in processes which deposit a metal on a substrate from a vapor phase, such as metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) and atomic layer epitaxy (ALE). They have the structure of formula II:
MLnxc2x7pDxe2x80x83xe2x80x83(II)
wherein
M is a metal chosen from the group consisting of: Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Y, La, Ce, Ti, Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, Mo, W, Mn, Re, Sm, Fe, Ru, Eu, Os, Co, Rh, Ir, Gd, Ni, Pd, Pt, Tb, Cu, Ag, Au, Dy, Ho, Al, Ga, In, Tl, Er, Ge, Sn, Pb, Tm, Sb, Bi, Yb, Lu, Th, and U;
D is a neutral coordinating ligand;
n is equal to the valence of M;
p is zero or an integer from 1 to 6; and
L is a ligand of formula III: 
wherein
R1 is alkyl, substituted alkyl, haloalkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, acyl, alkyl carboxylate, aryl carboxylate, alkenyl, alkynyl, or E2(R6)(R7)(R8);
R2 is H, halogen, nitro, or haloalkyl;
E1 and E2 are independently Si, Ge, Sn, or Pb;
R3, R4, R5, R6, R7, and R8 are independently chosen from alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, arylalkyl, alkoxy, alkenyl, alkynyl or R4 and R5, or R7 and R8 taken together form a divalent alkyl radical;
Y and Z are independently O, S or NR9; and
R9 is alkyl, substituted alkyl, cycloalkyl, aryl, substituted aryl, heteroaryl, arylalkyl, alkoxy, alkenyl, or alkynyl.
Preferred metals are Cu, Co, Mn, Ag, In, Ce, Sr, Ba, Ru, or Au. More preferred metals are Cu and Ag. In some embodiments, Pd and Pt are preferred metals. Preferred ligands are the preferred organometalloid compounds described above. In particular, ligands of formula IIII, wherein R1 is methyl, ethyl, isopropyl, n-propyl, isobutyl, s-butyl, n-butyl, CF3, C2F5, i-C3F7, n-C3F7, or xe2x80x94C(CH3)(CF3)2; R2is H; E1 independently C6 or lower alkyl; and Y and Z are O, may be used. xcex1-Gerrna-xcex2-diketones (formula III, where E1 is Ge) may also be used.
Ligands having reduced oxygen content can reduce oxygen contamination of the substrate during metal deposition. Preferred metal complexes are listed in Table 2:
The term xe2x80x9ccomplexxe2x80x9d is intended to be broadly construed to encompass compounds as well as coordination complexes wherein at least one metal atom is covalently, ionically or associatively coordinated to at least one organic ligand group. Accordingly, the metal complexes of the present invention may contain one or more neutral coordinating ligands (D in formula II) in addition to the organometalloid ligands described above, in particular when the metal has a valence of one. Suitable coordinating ligands include Lewis bases such as vinyltrimethylsilane (VTMS), bis-(trimethylsilyl) acetylene, 1,5-cyclooctadiene (COD), 1,6-dimethyl-1,5-cyclooctadiene, alkyl phosphines, alkynes, such as trimethylsilylalkyne (RMSA) and mixtures thereof.
In another embodiment, the present invention relates to metal complexes with fluorinated ligands, that is, where R3, R4, R5, R6, R7, and R8 are independently chosen from alkyl and haloalkyl, and at least one of R3, R4, R5, R6, R7, and R8 is haloalkyl. These complexes exhibit unexpected order in the solid state, in particular where E1 is Si and at least one of R3, R4, or R5 is C3 or higher fluoroalkyl. This is illustrated by the crystal structure of a complex where M is copper, R3 and R4 are methyl and R5 is (CH2)2(CF2)7CF3, as determined by x-ray diffraction. The structure is shown in FIG. 1. It can be seen from the figure that the perfluoroalkyl groups of one molecule associate with the perfluoroalkyl groups of other molecules in an orderly, interdigitated manner. The result is formation of a distinct fluorous region in the crystal.
Nanostructured materials composed of these complexes may contain separate fluorine- and/or metal-containing regions, domains, areas or layers, depending on the composition of the complex(es) employed, and method of fabricating the nanostructured materials. These regions may have oxophilic, fluorophilic, lipophilic and/or hydrophilic properties, and are, therefore, are useful in many applications. Fluoroalkyl domains are typically optically transparent and possess low k properties. Nanostructured materials having such domains may be used as nanoscale slits for microelectrooptical devices or as micromagnetic domains for data storage. Where self-organized Langmuir Blodget films are formed, the nanostructured materials may be used as magnetically sensitive thin films. In addition, the materials may be useful as organized catalysts. For example, a fluorocarbon interlayer may facilitate selective accumulation of reactants in oxidative transformations where the oxidized product might be protected from overoxidation due to limited solubility of the more polar product in the fluorous or fluorophilic phase. In particular, where the nanostructured material consists of a bimetallic catalyst created by combination of a mixture of two or more complexes, such as a mixture of a copper complex with a palladium complex, thin film catalysts for oxidative transformations may be formed.
Synthetic methods for the preparation of xcex2-diketones are numerous and well documented. However, application of these strategies to the synthesis of silyl xcex2-diketonates is frequently unsuccessful, due to the reactivity of the product to the reagents or reaction conditions, and to the occurrence of side reactions via the cleavage of the carbonyl-silicon bond. Therefore, it is preferred that the organometalloid compounds of the present invention be prepared by the processes of the present invention.
The organometalloid compounds may be prepared by a Claisen condensation between a lithium enolate anion and an acyl, thioacyl or imino compound having a leaving group adjacent to the unsaturated group. This reaction is illustrated in Scheme 1: 
In Scheme 1, R1, R2, R3, R4, R5, R6, R7, R8, R9, E1, Y and Z are as defined for the compounds of formula I, above, R is alkyl, and Q is a leaving group. Suitable leaving groups for the process are halo, acyl, alkoxy, phenoxy, amido, dialkylamino, and alkoxyamino. Preferably, R1C(Y)Q is an acid chloride or an ester. In the synthesis of non-fluorinated silyl-xcex2-diketones, R1C(Y)Q is preferably an acid chloride. The procedure may also be used for the synthesis of fluorinated derivatives, that is, where one or more of R1, R3, R4, or R5 are fluoroalkyl groups. Yields are typically lower than with non-fluorinated derivatives, presumably because of the enhanced acidity of the fluorinated xcex2-diketonates and the pursuant rapid protonation of the enolate. Therefore, it may be desirable to employ a variation of the process of Scheme 1, illustrated in Scheme 1a, for the preparation of fluorinated xcex2-diketones. In this procedure, base is added to a mixture of the two starting materials. Either lithium diamine (LDA) or NaH may be utilized as bases. Even in the presence of good electrophiles, the desired xcex2-diketones may be formed. When the perfluoroacid ester or acid fluorides were employed instead of acid chlorides at elevated temperature (xe2x88x9220xc2x0 to xe2x88x9240xc2x0 C.), higher yields of the fluorinated xcex2-diketones, with almost complete consumption of the starting acylsilanes, resulted. 
In another embodiment, the organometalloid compounds are prepared as illustrated in Scheme 2. A thioketal-protected acylmetalloid is reacted with an alkyllithium compound, such as n-butyl lithium, and the product is subsequently reacted with a copper salt to form a protected lithium dithianylmetalloid cuprate. The cuprate is then reacted with an appropriate xcex1-bromoketone or xcex1-bromo-thioketone. The thioketal protecting group can be removed by methods described in the literature. Preferably the deprotection is accomplished by treatment with a suitable mercury reagent. An example of an effective mercury reagent is a combination of mercuric oxide and mercuric chloride. 
The metal complexes of the present invention may be prepared by reacting the organometalloid compounds synthesized as described above with a metal salt under protic or aprotic conditions. The ligand is dissolved in a suitable solvent and the anion of the ligand is formed by abstraction of a proton with base. The metal salt is then added, and the resulting metal ligand complex is isolated by removal of the solvent and crystallized. Under protic conditions, a protic base such as sodium hydroxide, may be used, with a protic solvent, such as an aqueous alcohol. Similarly under aprotic conditions, aprotic bases and solvents may be used. An example of a suitable aprotic solvent is tetrahydrofuran; an example of a suitable aprotic base is potassium hydride.
In another embodiment, the metal complexes may be prepared directly as shown in Scheme 3. 
In Scheme 3, R1, R2, R3, R4, R5, R6, R7, R8, R9, E1, Y and Z are as defined for the compounds of formula III, above, and R is alkyl or phenyl. The starting lithium metalloid compound of formula E1R3R4R5Li is prepared according to the method described in the literature(Still, W. C., J. Org. Chem., 41, 3063-3064 (1976)). The lithiummetalloid compound is then reacted with an appropriate compound, as depicted in Scheme 3, for example, a xcex2-diketone, a xcex2-thioketone, or a xcex2-ketoimine, to yield a ligand of formula III. Without isolating the product, a metal salt is added to form a complex of the metal with the ligand.
Acylgermane compounds for use in synthesis of xcex1-germa-xcex2-diketones may be prepared via the metallation of ethyl vinyl ether. Scheme 4 illustrates a process in which acetyl trimethylgermane is prepared from ethyl vinyl ether and chlorotrimethyl-germane. Chlorotrimethylgermane, alternately listed as trimethylgermanium chloride, is commercially available, for example, from Aldrich. xcex1-Germa-xcex2-diketones may be synthesized by the procedures described for the synthesis of the xcex1-sila-xcex2-diketones, including those illustrated in Schemes 1 and 1a, and particularly by that in Scheme 1. Similarly, metal complexes with xcex1-germa-xcex2-diketones may be prepared by the methods shown in Schemes 2 and 3.
Processes whereby metals are deposited from volatile precursors are utilized in many different microelectronics applications. Metals such as Li, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Y, La, or Ce are typically used in applications such as high k dielectrics, superconductors, and high refractive index materials, although their use is not limited to these applications. Metals such as Ti, Zr, Hf, Pr, V, Nb, Ta, Nd, Cr, Mo, W, Mn, Re, or Sm are typically used in microelectronic applications chemically combined with nitrogen or silicon as the nitride or silicide for use as barrier materials or hard coatings, although, again, their use is not limited to these applications. Metals such as Fe, Ru, Eu, Os, Co, Rh, Ir, Gd, Ni, Pd, Pt, Tb, Cu, Ag, Au, Dy, Zn, Cd, Hg, Ho, Al, Ga, In, Tl, and Er are typically used in electronics applications as metals, or metal alloys, in particular, as metal or metal alloy films for interconnects, electrodes, and mirrors, although, again, their use is not limited to these applications. Metals and metalloids such as Si, Ge, Sn, Pb, Tm, Sb, Bi, Yb, and Lu are typically used in microelectronic devices and as semiconductors, although, again, their use is not limited to these applications.
The metal complexes of the present invention may be deposited on a substrate to form a layer of one or more metals in the form of the metal or of particular inorganic compounds, for example as an oxide, a hydroxide, a carbonate, a silicide or a nitride. It will be apparent to a person skilled in the art that, if desired, he may use not only a particular compound of formula II but also mixtures of such compounds in which M, L, or both vary. A metal complex is advantageously decomposed in the vapor phase by a metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE) or atomic layer epitaxy (ALE) process. The principle of these processes and suitable apparatuses for these purposes are well known in the art.
Typically, an apparatus for deposition from the vapor phase is pressure tight and can be evacuated. The substrate which is to be coated is to be introduced into this apparatus. Under reduced pressure the complex of formula II is vaporized. If desired, inert or reactive gas may be present in the apparatus in addition to the complex of the present invention in the vapor state.
The metal complex, in vapor form, is typically continuously or intermittently introduced into the apparatus via a special line. In some cases the metal complex may be introduced into the apparatus together with the substrate which is to be coated and not vaporized until it is within the apparatus. A carrier gas may optionally be used to aid in transporting the metal complex into the apparatus. The vaporization of the metal complex can be promoted by heating and if desired by the addition of the carrier gas.
Decomposition of the substrate may be effected by known methods. In general, these are thermal decomposition, plasma-or radiation-induced decomposition and/or photolytic decomposition. Thermal decomposition from the vapor phase is usually performed so that the walls of the apparatus are kept cold and the substrate is heated to a temperature at which the desired layer is deposited on the substrate. The minimum temperature required for decomposition of the compound may be determined in each case by simple testing. Usually, the temperature to which the substrate is heated is above about 80xc2x0 C. The substrate may be heated in a conventional manner, for example, by resistance heating, inductive heating, or electric heating, or the substrates may be heated by radiation energy. Laser energy is particularly suitable for this. Laser heating is particularly advantageous in that lasers can be focused, and therefore can specifically heat limited areas on the substrate.
An apparatus for thermal chemical vapor deposition is typically pressure tight such as are used in high vacuum techniques as this process is typically carried out under reduced pressure. The apparatus may comprise gas lines which can be heated for carrying the metal complexes or the inner gas, blockable gas inlets and outlets, temperature measuring means if decomposition is to be induced by radiation, a radiation source must also be present. In operation, the metal complex is introduced into the apparatus in the vapor phase. An inert or reactive carrier gas may be included.
Decomposition of the metal complex may be brought about as discussed above. For example, the decomposition may be plasma induced by a D.C. plasma, high-frequency plasma, microwave plasma or glow discharge plasma. Alternately photolytic decomposition may be effected by using a laser operating at a suitable wavelength.
The thickness of the layer deposited typically depends on the length of the deposition, on the partial pressure in the gas phase, on the flow rate of the gas and on the decomposition temperature. Depending on the desired layer thickness, a person skilled in the art can readily determine the time and deposition temperature required to produce a layer of a given thickness by simple tests.
If the metal complex is decomposed under an atmosphere of an inert gas, for example, argon, metal-containing layers are typically deposited in which the metal is essentially metallic form. The decomposition may also be carried out under a reactive gas atmosphere, including a reducing atmosphere, an oxidizing atmosphere, and a hydrolyzing or carbonizing atmosphere. A reducing atmosphere with hydrogen as the reactive gas is typically used for deposition of layers containing metals, for example, copper. Where the decomposition is carried out under an oxidizing atmosphere, for example, one containing oxygen, nitrogen dioxide or ozone, layers containing the metal in the form of an oxide are formed. Alternatively, it is also possible to operate in a hydrolyzing or carbonizing atmosphere, for instance, in the presence of water and/or carbon dioxide. The metal carbonate or hydroxide which is produced as an intermediate stage may be subsequently calcined to form the metal oxide. In addition, use of ammonia as a reactive gas yields layers containing the metal in the form of a nitride.
The process according to the invention is also suitable for depositing layers which contain one or more metals. In this case, the deposition process is characterized in that for depositing layers containing more than one metal, one or more compounds of formula II or other formulas are decomposed simultaneously or successively.